Source / drain contacts in organic polymer thin film transistors
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L6.2.1
Source / drain contacts in organic polymer thin film transistors Sandrine Martin, Michael C. Hamilton and Jerzy Kanicki* The University of Michigan, Department of Electrical Engineering and Computer Science, Solid-State Electronics Laboratory, 1067 BIRB, 2360 Bonisteel Blvd, Ann Arbor, MI 48109-2108, USA. ABSTRACT Organic polymer based thin-film transistors (OP-TFTs) look very promising for flexible organic electronics. In this paper, we describe devices based on a gate-planarized structure and using spin-coated organic polymer. We have analyzed the role of the device source and drain contacts and we present data indicating Schottky behavior of the contacts in OP-TFTs. In addition, we describe a quantitative evaluation of the source drain series resistances and extract the OP-TFT intrinsic electrical parameters. 1. INTRODUCTION Organic semiconductors can be divided into three main groups: small molecules, oligomers and polymers [1]. In general, oligomers deposited by evaporation in vacuum have a highly ordered molecular structure while most of the time, organic polymers are deposited by spin coating or inkjet printing over large areas at low temperature [2]. Organic polymer thin-film transistors usually show lower electrical performances than oligomer-based devices [1] but have a considerable potential in large-area low-cost flexible electronics. Although, so far, the electrical performances of most organic polymer thin-film transistors (OP-TFTs) are often limited by the polymer low conductivity, the source and drain contacts play a predominant role in the device operation. 2. DEVICE FABRICATION So far, many research groups have often used test structures, in which no patterning of organic and inorganic (especially gate electrode and insulator) layers is involved. We have fabricated and characterized gate planarized organic polymer thin-film transistor based on the structure shown in Figure 1 [ 3 ]. The organic semiconductor used here is solution-based F8T2 (poly-9,9dioctylfluorene-co-bithiophene) [4,5,6 ]. The OP-TFTs use benzocyclobutene (BCB) as gate planarization material, amorphous silicon nitride as gate insulator and ITO as source and drain electrodes. Our typical TFT channel width and length are 50-100 and 6-100 µm, respectively. 3. RESULTS AND ANALYSIS In this study, the OP-TFT source is always grounded, as shown in Figure 1. VDS
ID
Organic polymer source
drain
ITO a-SiNx:H
gate
BCB SiO2 coated c-Si
VGS
Cr
Figure 1: Cross section of our gate planarized OP-TFT structure. *
Also with the Center for Polymers and Organic Solids, University of California, Santa Barbara, CA (sabbatical).
Downloaded from https://www.cambridge.org/core. Rice University, on 16 May 2020 at 19:15:22, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-771-L6.2
L6.2.2
1.2
0
VGS = 1.0 -1
dIDS / dVDS (10 Ω )
-5
IDS (nA)
-15
F8T2 W=56µm L=16µm
VGS = -40V -30V -20V -10V
-20 -25 -40
0.8
-9
-10
-40V -30V -20V -10V
-30
-20
-10
0.6 0.
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